Silicon carbide and silicon carboxide fibers have many applications as high temperature structural materials. One method of preparing such fibers is that disclosed by Yajima et al. in U.S. Pat. No. 4,283,376. The method disclosed in the '376 patent produces a polycarbosilane which contains some siloxane bonds by adding a polyborosiloxane to a polysilane as shown below. ##STR1## It is stated by the patentee that this reaction gives a polycarbosilane containing the following structural units: ##STR2## where R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represent methyl, phenyl or hydrogen. Only a small number of the B structural units are present in the polycarbosilane. This polycarbosilane can be spun into a fiber and fired at 800.degree. to 1800.degree. C. in vacuum or an inert atmosphere to give a silicon carbide fiber.
Another method for producing silicon carbide fibers is disclosed in U.S. Pat. No. 4,100,233. This involves preparing an organosilicon high molecular weight compound with silicon and carbon as the main skeleton components. This compound is produced by the polycondensation of compounds which contain: 1) only Si-C bonds; 2) Si-H and Si-C bonds, 3) Si-Halogen bonds, 4) Si-N bonds, etc. Once the high molecular weight organosilicon compound is formed it is melted, spun into a fiber and heated to give a silicon carbide fiber.
Further, Great Britain Patent No. 1,359,576 discloses a method of forming a silicone fiber which involves the hydrolysis of organoalkoxy-silanes, followed by mixing the hydrolyzed silane with polyethylene oxide, spinning this mixture and then heating above 600.degree. C. This produces a quartz fiber (SiO.sub.2) which contains carbon.
Finally, chemical vapor deposition (CVD) using a gaseous mixture of hydrogen, argon and chlorosilanes can be used to prepare silicon carbide fibers. Usually monofilament carbon fibers are used as the core fiber. The vapors are fed into a reactor at about 1300.degree. C. and the carbon fiber placed therein, resulting in the deposition of SiC onto the core fiber. This method is very expensive.
The instant invention differs significantly from the prior art described above and also offers some advantages. First, the instant invention relates to a continuous silicon carboxide fiber (hereinafter referred to as a black glass fiber) versus silicon carbide or quartz fibers of the prior art. The black glass fibers of the present invention are resistant to oxidation at temperatures as high as 1350.degree. C. This has previously not been observed of a fiber containing a substantial amount of carbon.
The instant invention also provides a method of forming the black glass fiber. This method involves first preparing a cyclosiloxane polymer in solution, then spinning a fiber and finally pyrolyzing the fiber in a non-oxidizing atmosphere to give a black glass fiber. Specifically, the cyclosiloxane polymer is prepared by reacting a silicon hydride group (Si-H) with a silicon olefinic group, e.g. Si--CH.dbd.CH.sub.2, in the presence of a catalyst to form an ethylene linkage as shown below: EQU .tbd.Si--H+CH.sub.2 .dbd.CH--Si.tbd..fwdarw..tbd.SiCH.sub.2 CH.sub.2 Si.tbd .
This reaction is known as hydrosilylation and the catalyst employed is known as a hydrosilylation catalyst.
The hydrosilylation reaction differs from the reactions of the prior art which are used to prepare a polymer in, the following ways. The '376 patent involves reacting a polysilane with a polyborosilane to give a polycarbosilane and an alkyl boron or boron hydride as a side product. In contrast to this reaction, the hydrosilylation reaction of the instant invention does not involve any boron in the reaction and no side product, i.e., boron hydride, is produced. The hydrosilylation reaction is an addition reaction, i.e. adding hydrogen to a double bond.
The reaction described in the '233 patent is also different from the hydrosilylation reaction. The '233 patent describes a polycondensation reaction which involves producing radicals of the monomer which radicals then combine (via new Si-C bonds) into an organosilicon polymer with the elimination of a gas such as methane, hydrogen, etc. Again the hydrosilylation reaction does not form any byproduct gas and no new Si-C bonds are formed.
Finally, comparing the instant reaction with that of the '576 patent, it is noted that the '576 patent involves a hydrolysis reaction. There is no water present in the hydrosilylation reaction end thus, these two reactions are completely different.
Once the polymer is formed, it can be formed into a fiber by spinning the polymer. This fiber is now hardened by passing it through a hot zone and then pyrolyzed under a non-oxidizing atmosphere to give a black glass fiber having the formula SiC.sub.x O.sub.y where x ranges from about 0.5 to about 2.0 and y ranges from about 0.5 to about 2.0. Thus, the instant invention provides a black glass fiber and a method of producing a black glass fiber in which the amount of carbon and oxygen in the fiber can be readily controlled.